Trailer hitches are devices which connect a tow vehicle to a trailer by means of a ball hitch which is mounted onto the vehicle, or onto a tow bar which is connected to the vehicle. The hitch then mates with a hitch ball socket. This ball and socket configuration is designed to allow adequate rotation of the socket with respect to the ball so that the vehicle-trailer combination can maneuver around corners. Typically the socket mechanism has a releasably lockable coupling so that it locks onto the ball hitch to prevent decoupling while towing.
There are several standardized sizes of these ball and socket systems, the specific size usually depends on the size of the trailer or its weight and is specified by the outer diameter of the hitch ball. Typical ball sizes are diameters of 1⅞ inches, 2 inches, 2¼ inches, and 2{fraction (5/16)} inches. For a trailer hitch to function properly and safely, it is important that the size of the ball matches that required by the particular hitch socket. Using a ball that is smaller than the size specified for the trailer could have disastrous consequences, and coupling a trailer with a ball that is too large for its socket is impossible. A vehicle may need to tow a variety of trailers, with sockets of different sizes, and hence there is a need to be able to employ different sizes of hitch balls on a vehicle.
Conventional hitch balls include a mounting bolt and ball as an integral unit. The unit is bolted onto the tow bar and requires at least one wrench for its removal and installation. This can be inconvenient because it requires that one carry the proper tools in the vehicle, as well as a variety of hitch balls, which can have their threads damaged if not properly stored. Additionally, the hitch ball mounting threads may become corroded or filled with debris so that removing the ball can be a formidable task, especially when trying to change a hitch ball at night in the rain. It is usually not feasible to have multiple, different-sized balls bolted to a vehicle because the ball must be located along the centerline of the vehicle and at a preferred height in order to evenly distribute the loads acting on the vehicle and trailer.
With the purpose of overcoming these problems, several types of hitches, which present other schemes of interchanging balls, have been invented. For example, U.S. Pat. No. 4,433,854 issued Feb. 28, 1984 to Smith shows an interchangeable ball hitch in which the ball contains a spring-biased latch that locks the ball onto a mounting piece which is attached to the tow bar and which can be released for interchanging the ball sizes. The latch includes a spring and pin which are integral to the mounting piece. This device requires that the ball be rotated into the proper position for removal which can be difficult if trying to change a ball at night without a flashlight.
U.S. Pat. No. 5,169,168 issued Dec. 8, 1992 to Harry et al describes a hitch ball assembly including interchangeable balls and a mounting post which is attached to the tow bar. The mounting post contains a grooved path and the ball has a pin on the inner cavity of the ball. To mount the ball one must align the pin with the beginning of the groove at the top of the post and then rotate and depress the ball to move the pin along the groove until it has fully seated. Once seated, the ball is free to rotate around the mounting post. The pin can be damaged during towing by the trailer loads if the tolerances of the fit between the ball and post are too large or if the ball binds up in the hitch socket and then applies those extra loads to the post. In these instances a large portion of the trailer forces are being transferred to the vehicle through just the pin.
U.S. Pat. No. 5,419,576 issued May 30, 1995 to Van Vleet, describes an interchangeable ball hitch connector which includes an interchangeable ball and a mounting post which is bolted onto the tow bar. The ball has a chamber which the mounting post fits within. Both the ball and the post have holes which are aligned when the ball is in place and through which a locking pin is placed to hold the two parts together.
U.S. Pat. No. 5,871,222 issued Feb. 16, 1999 to Webb describes a detachable ball hitch apparatus which includes a ball hitch with an integral post that fits into the cavity of a piece that mounts onto the tow bar. The post has a spring-loaded pin that slides into a groove in the tow bar piece. When the ball is fully mounted the pin is depressed to lock it into the groove to prevent its unintentional removal. Once installed, the ball is not free to rotate. If the spring should fail, the ball cannot be easily removed from the tow bar. Also, the pin and spring are located inside of the ball so this device would be more expensive than others because each of the interchangeable balls must contain those pieces.
U.S. patent application Ser. No. 10/286,005 filed Oct. 31, 2002 by Smith, an inventor in the present application, describes an interchangeable hitch ball system which includes a threaded mounting post and hitch balls with partially threaded cavities. A hitch ball is mounted onto the post by engaging the threads and screwing the ball onto the post. Once the threaded portion of the cavity passes the mounting post threads, the ball is in fully mounted and is free to turn. The hitch ball is disengaged by lifting the ball and turning it to re-engage the threads and then unscrewing the hitch ball.
While the above-described structures teach the use of detachable and/or interchangeable hitch balls for towing applications, there remains a need for improved interchangeable hitch ball assemblies. This need manifests in both the need for simplified structures as well as structures that can be manufactured efficiently at a reduced cost. The present invention is directed to providing an improved construction for interchangeable hitch ball systems.